19-well double hexagon pattern for secondary recovery



April 30, 1968 A. F. ALTAMIRA ET AL 33 5 l9-WELL DOUBLE HEXAGON PATTERNFOR SECONDARY RECOVERY Filed June 28, 1966 4 Sheets-Sheet l -WW0 w April30, 1968 A. F. ALTAMIRA ET AL 3,380,526

IQ-WBLL DOUBLE HEXAGON PATTERN FOR SECONDARY RECOVERY 4 Sheets-Sheet 2Filed June 28. 1966 April 30, 1968 F, T R ET AL 3,386,526

lQ-WELL DOUBLE HEXAGON PATTERN FOR SECONDARY RECOVERY April 30, 1968 A.F. ALTAMIRA ET AL 3,380,526

l9-WELL DOUBLE HEXAGON PATTERN FOR SECONDARY RECOVERY Filed June 28,1966 4 Sheets-Sheet 4 United States Patent 3,380,526 19-WELL DOUBLEHEXAGON PATTERN FOR SECONDARY RECOVERY Anthony F. Altamira and Donald L.Hoyt, Houston, Tex.,

assiguors to Texaco Inc., New York, N.Y., a corporation of DelawareFiled June 28, 1966, Ser. No. 561,146 9 Claims. (Cl. 1669) Thisinvention relates generally to the production of hydrocarbons fromunderground hydrocarbon-bearing formations, and more particularly, to amethod for increasing the overall production of hydrocarbons therefrom.

In exploiting underground hydrocarbon-bearing formations through aplurality of wells, it has been the general practice that when aproduction well yields an excessive amount of an extraneous fluid otherthan the hydrocarbons, e.g., water or gas, that production well isshut-in and the production of hydrocarbons is started and carried out atother production wells in the field. It is known that in such instances,a substantial amount of hydrocarbons is left behind in thehydrocarbon-bearing formation since such is not considered primarilyrecoverable economically.

Secondary recovery operations are now an essential part of the over-allprogram planning for virtually every oil and gas-condensate reservoir inunderground hydrocarbon-bearing formations. Some of the operationsdeveloped include g-as repressuring and water, fire, steam and solventflooding. Usually, they all employ some geometric pattern of injectionand production wells, with injection of fluid into some of the Wells todisplace hydrocarbons in the reservoir zone toward the production wells.

The front, or interface, between the injected and inplace fluids movesfrom injection toward production wells, changing shape as it progresses.Due to the pressure sinks around the production wells, a portion of theinterface tends to accelerate and cusp into the production wells.Breakthrough of the injected fluid occurs when the interface reaches theproduction wells. The percentage of the entire reservoir which has beeninvaded by the injected fluid at that time is referred to as the sweepefficiency of the particular geometric pattern used.

The most commonly used well pattern is secondary recovery in the 5-spotpattern, with four injection wells at the corners of a square and aproduction well at the center. In a production field of 5-spot patterns,there are as many injection wells as production wells. Sweep efliciencyfor the S-spot pattern is about 71 percent. Other basic flood patternssometimes used are the 7-spot, direct line and staggered line drives,with sweep efficiencies of 74, 57 and 78 percent respectively.

In field practice, injection usually will be continued well pastbreakthrough until the reservoir cannot be produced economically. Inthis way, some additional sweepout can be achieved, but often there willbe large volumes of produced injection fluid to be handled, treated andre-injected. If sweepout prior to breakthrough in a pattern flood wereimproved, it is very likely that the ultimate recovery would be higher.The time and cost of the operation, to achieve comparable recoveries,would be reduced accordingly.

Accordingly, it is an object of the present invention to provide animproved method for the production and recovery of hydrocarbons,particularly liquid petroleum, from underground hydrocarbon-bearingformations.

Another object of this invention is to provide a method whereby the areasweep efficiency in pattern flooding is improved.

These and other objects, advantages and features of ice this inventionwill become apparent from a consideration of the specification withreference to the figures of the accompanying drawings wherein:

FIG. 1 discloses a conventional 5-spot pattern unit in a fieldundergoing secondary recovery illustrating the interface of the injectedfluid at breakthrough at the production wells;

FIG. 2 discloses the formation of a 19-well double hexagon pattern unitin a field of staggered equidistantly spaced wells;

FIGS. 3, 4 and 5 illustrate the movements of the interface of theinjected fluid during the three phases of the exploitation plan in one19-Well double hexagon pattern unit in a field undergoing secondaryrecovery; and

FIGS. 6, 7, and 8 illustrate the movements of the interface of theinjected fluid during the three phases of an alternate exploitation planin one 19-wel1 double hexagon pattern unit in a field undergoingsecondary recovery.

In our copending, coassigned application for patent Ser. No. 517,052,field Dec. 28, 1965, for Interface Advance Control in Pattern Floods byUse of Control Wells, there is disclosed how an increased amount ofhydrocarbons is produced and recovered from an undergroundhydrocarbon-bearing formation by employing at least three wells,penetrating such a formation, which wells can be in-line, to producehydrocarbons from the formation via two of these wells including themiddle well, as disclosed in the co-assigned US. Patent No. 3,109,487,issued to Donald L. Hoyt, on .Nov. 5, 1963.

It is understood that the failure of the driving flood in secondaryrecovery operations to contact or sweep all the hydrocarbon area is dueto the development, in the interface, of a cusp which advances towardthe production well. If other portions of the interface could be made tokeep up, or if the cusp formation were delayed, complete area sweepwould be possible. In the above cited co-assigned application, aproduction control well is positioned between the injection well and theproduction well and is kept on production even after the injection fluidreaches it. In this manner, the cusp is pinned down at the control welland while the area swept out by the injection fluid before breakthroughat the last production well is increased, there is an unwanted handlingof considerable quantities of injection fluid at the control well.

Another aspect to increase the sweepout efli'ciency is disclosed in ourcopending, coassigned application for patent Ser. No. 516,891, filedDec. 28, 1965, for Interface Advance Control in Pattern Flods byRetarding cusp Formation, and involves the retardation of thedevelopment of the cusp forward the production well. The method ofachieving more uniform advance is to control the flow gradients so thatthe interface is spread out. This can be done either by choosing aparticular geometry of well positions or by adjusting the relativeproduction rates so that the velocity of advance is not predominantly inone direction. It can be done also by shifting the gradients frequently,in both direction and magnitude, thus preventing any one section of aninterface from advancing too far out of line.

The figures of the drawings schematically disclosed and illustrate thepractice and the advantages of our invention with well pattern and arealsweepout examples which are obtainable and have been observed both insecondary re covery operations and in potentiometric model studies whichsimulate secondary recovery operations. The model studies indicate asweepout obtained in and ideal reservoir, although the recovery from anactual sweepout of a particular field may be greater or less, dependingon field parameters. The procedures to be described are based on thefollowing set of experimental conditions and assumptions:

(1) All the units in any patern are balanced and produce at the samerate. This requires that wells on the edges of a pattern unit produce orinject at /6 or /2 of the rate of interior wells, depending inversely onthe number of pattern units with which they are associated;

(2) The total amount of fluid injected must be equal to the fluidproduced for each pattern unit, as well as for the whole pattern;

(3) The mobility ratio of the displacing to the displaced fluid is 1.0;

(4) The permeability and sand thickness of the formation is uniform; and

(5) Gravitational effects are not considered.

Throughout the drawings, the same symbolic indicators will be maintainedas follows: R P P andl represent respectively, production wells at thecorners, along the sides, medially and the center interior wells; and, asolid circle indicates a production Well, a crossed circle indicates ashut-in well, and an arrowed circle indicates an injection well.

FIG. 1, illustrates the interface of the injected fluid at breakthroughat the well of a single conventional S-spot pattern unit in a productionfield undergoing secondary recovery, wherein .the corner wells of eachpatern unit are injection wells, while the inner center well is used forproduction. Such a procedure will produce a sweepout of approximately71%. In this pattern, the ratio of the distance between the rows ofwells to the distance between the in-line wells is 0.5, i.e. d/a= /2.

Referring to FIG. 2, there is disclosed the formation of a 19-welldouble hexagon pattern, comprising six wells (P located at the verticesof an inner equilateral hexagon and a similar, concentric outer hexagonhaving wells (P located at the vertices thereof, and midway betweenthese, wells (P on the sides of the outer hexagon, and a single centralwell (P,). The wells at the vertices and on the sides are part of astaggered equidistant well spacing, the ratio of the distance betweenthe rows of wells to the distance between the in-line wells being 0.866,i.e. d/a=0.866. The wells at the vertices of the hexagons lie on commondiagonals passing through the central well, with the wells (P at thevertices of the inner hexagon being located medially between the cornerwells (P of the outer hexagon and the control well (P FIGS. 3, 4 and 5disclose the interface shapes at the ends of the consecutive steps ofthe three phase, secondary recovery exploitation plan as used in the19-well double hexagon pattern.

FIG. 3 discloses the interface shape at the end of the first phase,wherein driving fluid is injected into the formation through the wells(P along the sides of the outer equilateral hexagon, with production atthe wells (P at the corners or vertices thereof until breakthrough ofthe injection fluid occurs thereat. The remaining wells of the patternunit are shut in during this phase of the plan. At this breakthrough, asubstantially hexamerous camlike area, having an outline of a spur gear,defined by the cusp formation ending at the producing corner wells (Premains, and is indicated by cross-hatching in FIG. 3, with an areasweepout of 30%. The ratio of the injected well rate to the productionwell rate is 2 to 3 i.e. there are two production wells for each threeinjection wells. Both injection and production are uniformlydistributed.

FIG. 4 discloses the interface shape at the end of the second phase ofthe exploitation plan wherein injection is shifted from the side wells(P which are shut in now, to the corner wells (P of the outer hexagon,production is initiated both at the medial wells (P at the vertices ofthe inner hexagon and at the central well (P and maintained untilbreakthrough occurs at the medial wells (P of the fluid injected intothe formation, the symbolic indicators being used as noted previously.An additional 38% sweepout is attained to give a sub-total of 68% sweepefficiency. The ratio of the injection rate to the production well rateis 7 to 2, i.e. there are seven production wells for each two injectionWells, with the injection and production rates being uniformlydistributed.

The unswept area at the end of the second phase, as disclosed in FIG. 4,is hexagonal in shape with individual pairs of ear-like areas extendingfrom the vertices thereof. The shift of injection from the side wells (Pwhich are shut in, to the corner wells (P and the resultant productionfrom the remainder of the wells in the pattern unit have extendedgreatly the interface so that at the end of the second phase,breakthrough at the medial wells (P occurs almost from two directions atthe same time.

FlG. 5 discloses the interface shape at the end of the third phase ofthe exploitation plan. As in the second phase, injection is maintainedat the corner wells (P of the outer hexagon with the sides wells (Pthereof being shut in, production at the medial wells (P is stopped andand these wells are shut in, and production is maintained at the centerwell until breakthrough of the injection fluid thereat. The final shapemay be described as a web of Y-shape areas, with the stems of the Ydefining a hexafoil based on the center well. An additional 26% sweepoutis attained to give a total of more than 94% sweep efiiciency.

FIGS. 6, 7 and 8 disclose the interface shapes at the ends of theconsecutive steps of an alternate three phase, secondary recovery planas used in the 19-well double hexagon patern, with both injection andproduction rates being uniformly distributed.

FIG. 6 discloses the interface shape at the end of the first phase ofthis alternate plan, wherein driving fluid is injected into theformation through the center well (P,), with production from theremaining wells of the unit, viz. at the wells (P P at the corners orvertices and midway along the sides of the outer equilateral hexagon,and at wells (P at the corners or vertices of the inner hexagon, untilbreakthrough of the injeoted fluid occurs at the latter. At thisbreakthrough, a substantially circular area defined by cusps ending atthe medial wells (P has been swept out for a 25% sweep efficiency,resulting from an injection well to production well ratio of 1 to 11.

FIG. 7 discloses the interface shape at the end of the second phase ofthe alternate plan, wherein injection is maintained at the center well(P production from the corner wells (P P of both hexagons is stopped andthese wells shut in, and production continued from the side wells (P ofthe outer hexagon until breakthrough thereat. At this breakthrough, asubstantially hexamerous area defined by the cusp formations ending atthe production side wells has been swept and the area remaining forsweepout is indicated by crosshatching in FIG. 7, for an area sweepoutsub-total of 64%. The ratio of the injection well rate to the productionwell rate is 3 to 1, i.e. there are three production wells for eachinjection Well.

FIG. 8 discloses the interface shape at the end of the third phase ofthe alternate plan, wherein the center well (P and the medial wells (Pat the corners of the inner hexagon are shut in, production from theside wells (P is discontinued and injection is initiated thereat, andproduction is initiated and maintained at the corner wells (P untilbreakthrough thereat. The unswept areas are indicated by crosshatchingin the shape of fishtails based on the corner production wells,indicating a sweepout of over 88%. The ratio of the injection rate tothe production rate is 2 to 3, i.e. there are two production wells foreach three injection wells.

As in the case of the preferred exploitation plan as depicted in FIGS.3, 4 and 5, the unswept areas are located around the production wells,in areas having the strongest flow gradients. Thus, further productionmay be continued after breakthrough with comparatively less productionof the injected fluid than in the ordinary production followingbreakthrough, to give sweepouts greater than those indicated above.

It is recognized that any of the increased sweepouts obtained by the useof 19-well double hexagon pattern exploited as disclosed herein is anidealization, as in the case for the sweepouts for the 5- and 7-spotpatterns. None of the values is likely to be achieved in the field, butthe relative superiority of the sweepouts thereover obtained by the useof the 19-well double hexagon pattern is clear and is independent ofinhomogeneities.

The basic technique employed to increase sweep efliciency controls theadvance of the front in the pattern to achieve large areal coverage, byshifting and adjusting the geometric position, direction and magnitudeof the flow of pressure gradients. If the positions of the wells in thepattern are favorable, by changing the wells used for injection andproduction, high flow gradients can be made to cover most of thepattern, The pattern and procedures disclosed herein have high sweepefliciency leaving the unswept areas at breakthrough in the regions ofstrong flow gradients adjacent the production wells, and thus readilyswept by production past breakthrough.

The sweepout and volumes of injected fluid produced vary from onepattern to another, and also appear to be functions of rate distributionand distance parameters within a given pattern.

In evaluating the performance of a flood pattern, or in comparingperformances of different patterns, there are three main considerations:

(a) Percentage of sweep (b) Volume of injection fluid handled (c) Timeto achieve the sweep.

For a given total field production rate, it will not be possiblegenerally to obtain an increase in sweepout without at least aproportionate increase of time, which is to be expected. However, if theextra time involved is disproportionately long, the gain in sweepout maynot be economically worthwhile.

Any pattern and/or rate distribution which retards the development, orthe advance, of a cusp towards the production wells will increase thesweepout of a field. As mentioned previously, two principal means ofdoing this are: (a) pinning down the cusp by locating production wellsbetween the injection source and the outer production wells, and keepingthese inner (or control) wells on production after breakthrough, and (b)spreading out the cusp by pulling the front toward side wells untilbreakthrough thereat before allowing it to proceed toward the cornerproduction wells of a pattern unit, as disclosed in our above citedcoassigned applications.

The spreading out of the cusp is in general a more advantageousprocedure. It yields as good or better sweepout with less production orinjection fluid. Further, a higher rate distribution on corner wells ofpattern units generally results in much less overall production ofinjection fluid, but also in less sweep (although exceptions can befound in more complicated patterns).

The advantages of the methods disclosed above are evident. Fewerinjection wells are required, more reservoir fluid is recovered prior tobreakthrough of injection fluid, and so more ultimate recovery isobtained, as compared with other methods generally employed in secondaryrecovery operation.

Although emphasis has been placed in this disclosure on the practice ofthis invention as directed to a secondary recovery operation,particularly employing water or other similar aqueous fluid as theinjection fluid or displacement fluid, the advantages obtainable in thepractice of this invention are also realized in primary hydrocarbonproduction operations wherein the hydrocarbon-bearing formation is underthe influence of a water drive or gas drive, or both a water and a gasdrive, and also in the instance of a secondary recovery operationwherein a gas, such as natural gas, is employed as the injection fluid.

As will be apparent to those skilled in the art, in the light of theaccompanying disclosure, other changes and alternatives are possible inthe practice of this invention without departing from the spirit orscope thereof.

We claim:

1. A method of producing hydrocarbons from an undergroundhydrocarbon-bearing formation involving a pattern unit of wells locatedat the vertices and on the sides of a hexagon and wells locatedtherewithin including a central well which comprises introducing fluidinto said formation via the wells located on the sides of said hexagon,and producing hydrocarbons from said formation via the wells located atsaid vertices of said hexagon until breakthough of the fluid introducedinto said formation thereat, thereupon ceasing introducing fluid viasaid side wells and introducing fluid into said formation via the Wellsat said vertices of said hexagon and producing hydrocarbons via saidwells within said hexagon until breakthrough of said fluid introducedinto said formation into said last mentioned wells producinghydrocarbons other than said central well, and thereafter ceasingproducing hydrocarbons at the breakthrough wells while continuingproducing hydrocarbons via said central well until breakthrough of theintroduced fluid thereat.

2. In the method of producing hydrocarbons as defined in claim 1, therates of introducing fluid into said formation and producinghydrocarbons from said formation being controlled so that thebreakthrough of the fluid introduced into said formation at theproducing wells occurs simultaneously.

3. In the method of producing hydrocarbons as defined in claim 1, saidwells located at the vertices of said hexagon defining an outerequilateral structure, said wells located therewithin other than saidcentral well defining an inner similar hexagon.

4. In the method of producing hydrocarbons as defined in claim 3, saidwells located at said vertices and on said sides of the outer hexagonbeing spaced equally from each other on each of said sides, said centralwell being located equidistantly from the vertices of said inner similarhexagon, the wells in said pattern unit totaling 19 in number.

5. In the method of producing hydrocarbons as defined in claim 4, thewells located at said vertices and on said sides of said outer hexagonand therewithin being spaced apart and aligned in rows whereby the ratioof the distance between the rows of wells to the distance between thein-line wells is 0.866, defining a double hexagon pattern unit in aproduction field.

6. The method of producing hydrocarbons from an undergroundhydrocarbon-bearing formation involving wells located at the verticesand on the sides of similar concentric hexagons and a central welllocated therewithin which comprises injecting fluid into said formationvia the wells located on the sides of the larger of said hexagons, andproducing hydrocarbons from said formation via the wells located at saidvertices of said larger of said hexagons until breakthrough of the fluidinjected into said formation thereat, thereupon ceasing introducingfluid via said side wells and introducing fluid into said formationthrough the wells at end vertices of said larger of said hexagons andproducing hydrocarbons from said central Well and the wells defining thesmaller of said hexagons until breakthrough of said fluid injected intosaid formation in said last mentioned wells producing hydrocarbons otherthan said central Well, and thereafter ceasing producing hydrocarbons atthe breakthrough wells while continuing producing hydrocarbons at saidcentral well until breakthrough of the introduced fluid thereat.

7. In a method of producing hydrocarbons from an underground formationinvolving a pattern unit a production field comprising similarequilateral hexagons and a center well, with the outer of said hexagonshaving a well on each of its sides equally spaced from the verticesadjacent thereof, the steps of injecting fluid into said formationthroughout said center well and producing formation hydrocarbons fromthe remaining wells of said pattern unit until breakthrough of theinjected fluid at the production wells defining the vertices of theinner of said hexagons, thereupon ceasing production thereat and at thevertices of the outer of said hexagons while continuing injecting fluidthrough said center well and producing formation hydrocarbons from thewells located on said sides of said outer hexagon until breakthrough ofinjected fluid thereat, and thereafter ceasing injecting fluid at saidcenter well and producing formation hydrocarbons from the side wells ofsaid outer hexagon and initiating injecting fluid at said side wells andinitiating producing formation hydrocarbons from the wells at saidvertices of said outer hexagon until breakthrough of said injected fluidthereat.

8. In the method of producing hydrocarbons as defined in claim 7, therates of introducing fluid into said formation and producinghydrocarbons from said formation being controlled so that thebreakthrough of the fluid introduced into said formation at theproducing wells occurs simultaneously.

9. In the method of producing hydrocarbons as defined in claim 7, thewells located at the vertices of said hexagons and on each of the sidesof said outer hexagon and said center well being spaced apart andaligned in IO'WS whereby the ratio of the distance between the rows ofwells to the distance between the in-line wells is 0.866, defining adouble hexagon pattern unit totaling 19 wells in number.

References Cited UNITED STATES PATENTS 2,885,002 5/1959 Jenks 16693,113,616 12/1963 Dew et al 1669 3,113,617 12/1963 Oakes 1669 3,113,61812/1963 Oakes 1669 3,120,870 2/ 1964 Santourian 1669 3,143,169 8/1964Foulks 1669 3,205,943 9/ 1965 Foulks 1669 CHARLES E. OCONNELL, PrimaryExaminer.

D. H. BROWN, Assistant Examiner.

1. A METHOD OF PRODUCING HYDROCARBONS FROM AN UNDERGROUNDHYDROCARBON-BEARING FORMATION INVOLVING A PATTERN UNIT OF WELLS LOCATEDAT THE VERTICES AND ON THE SIDES OF A HEXAGON AND WELLS LOCATEDTHEREWITHIN INCLUDING A CENTRAL WELL WHICH COMPRISES INTRODUCING FLUIDINTO SAID FORMATION VIA THE WELLS LOCATED ON THE SIDES OF SAID HEXAGON,AND PRODUCING HYDROCARBONS FROM SAID FORMATION VIA THE WELLS LOCTED ATSAID VERTICES OF SAID HEXAGON UNTIL BREAKTHROUGH OF THE FLUID INTRODUCEDINTO SAID FORMATION THEREAT, THEREUPON CEASING INTRODUCING FLUID VIASAID SIDE WELLS AND INTRODUCING FLUID INTO SAID FORMATION VIA THE